Activated corrosion products assessment and minimization strategies investigated in the EUROfusion safety research program

In large primary heat transfer systems of water-cooled fusion machines, corrosion occurs under an intense radiation field. The Activated Corrosion Products (ACPs) formation and deposition are complex multi-physical processes. Corrosion/erosion phenomena may mobilize activated particles which are transported inside the whole cooling loop, causing the build-up of activated deposits outside the under-flux region. ACPs represent a significant radiological hazard, being potentially one of the major contributors to the occupational dose. Their mitigation in large primary heat transfer systems may provide benefits in terms of collective dose reduction, waste management, source term minimization and availability optimization. At ENEA, in collaboration with LEI, the University of Rome La Sapienza, Consorzio RFX, RINA-CSM and CEA, ACPs assessment and minimization strategies are investigated for watercooled fusion machines. A full calculation chain based on MCNP (Monte Carlo N-Particle) and the OSCAR-Fusion code (tOol for Simulating ContAmination in Reactors) is put in place for ACPs inventory estimation in tokamak water-cooled heat transfer systems. The ACPs calculated by OSCAR-Fusion are then used to define MCNP sources for gamma transport calculations and evaluate their impact on occupational dose in several fusion applications. The inventory of corrosion products in terms of mass, composition, oxide morphology and release rates is strictly connected to the design choices concerning water chemistry and structural materials. Experimental campaigns have been carried out to provide indications on the best water chemistry and on the corrosion rates for Reduced Activation Ferritic/Martensitic (RAFM) steels. The main purpose of this work is to provide a general overview of the simulation and experimental activities on ACPs formation carried out in the EUROfusion safety research program. Special attention is devoted to EU-DEMO ACPs production estimation and mitigation. Future needs on ACPs simulation code development and validation, water chemistry optimization and experimental data production on RAFM steel corrosion are finally discussed.